The increasing demand for low-latency, high-bandwidth connectivity has introduced novel challenges to delivering strong resilience guarantees in production network environments. Closed hardware platforms, known as middleboxes, that lack visibility and support for state retention remain a key challenge for continuous service delivery during network failures. These middleboxes rarely employ recovery mechanisms of their own, inspiring renewed interest in the field of NFV in recent years due to this gap within the industry. The increasing availability of VNF capabilities in modern infrastructures offers an opportunity to exploit the flexibility of software and use hybrid architectures to improve resilience. REMEDIATE is a high-availability service that propagates state between unmodified hardware middleboxes and backup PNF or VNF appliances. The platform utilises targeted packet mirroring to allow network devices to organically construct equivalent state and thus allow an easy transition between hardware and software. To demonstrate its viability, we have evaluated REMEDIATE against a wide range of common hardware middlebox use cases built using multiple open-source packet processing frameworks. Results show upwards of 90% matching state with no observable delay to normal traffic or impact on its functionality.

The increasing demand for low-latency, high-bandwidth connectivity has introduced novel challenges to delivering strong resilience guarantees in production network environments. Closed hardware platforms, known as middleboxes, that lack visibility and support for state retention remain a key challenge for continuous service delivery during network failures. These middleboxes rarely employ recovery mechanisms of their own, inspiring renewed interest in the field of NFV in recent years due to this gap within the industry. The increasing availability of VNF capabilities in modern infrastructures offers an opportunity to exploit the flexibility of software and use hybrid architectures to improve resilience. Katoptron is a high-availability service that propagates state between unmodified hardware middleboxes and backup PNF or VNF appliances. The platform utilises targeted packet mirroring to allow network devices to organically construct equivalent state and thus allow an easy transition between hardware and software. To demonstrate its viability, we have evaluated Katoptron against a wide range of common hardware middlebox use cases built using multiple open-source packet processing frameworks. Results show upwards of 90% matching state with no observable delay to normal traffic or impact on its functionality.

Resilience in networks has often relied on high availability to ensure minimal disruption to end users when faults occur, but this has grown difficult for retaining state with the growing popularity of hardware middleboxes – blackbox hardware network functions that have served as an important part of network design in recent years. There is potential room for the introduction of Network Function Virtualisation (NFV) in the field of resilience in connection with middlebox usage. Rather than relying on overprovisioning, we propose Middlebox Minion (MiMi) VNF, a system design that can be inserted around inaccessible hardware. This recreates state in accordance with the middlebox function, using NFV to establish stateful failover mechanisms without the need to replace existing hardware. The experiment we present is a failover analogy examining the importance of state retention and the complexities involved with inaccessible hardware. Results suggest a promising improvement of connection quality and up to 60% lower loss when state can be preserved across failover instances, as well as potential for further exploration of the topic area.

To assess the accuracy of individual tree crown (ITC) delineation techniques the same tree needs to be identified in two different datasets, for example, ground reference (GR) data and crowns delineated from LiDAR. Many studies use arbitrary metrics or simple linear-distance thresholds to match trees in different datasets without quantifying the level of agreement. For example, successful match-pairing is often claimed where two data points, representing the same tree in different datasets, are located within 5 m of one another. Such simple measures are inadequate for representing the multi-variate nature of ITC delineations and generate misleading measures of delineation accuracy. In this study, we develop a new framework for objectively quantifying the agreement between GR and remotely-sensed tree datasets: the Accuracy of Remotely-sensed Biophysical Observation and Retrieval (ARBOR) framework. Using common biophysical properties of ITC delineated trees (location, height and crown area), trees represented in different data sets were modelled as overlapping Gaussian curves to facilitate a more comprehensive assessment of the level of agreement. Extensive testing quantified the limitations of some frequently used match-pairing methods, in particular, the Hausdorff distance algorithm. We demonstrate that within the ARBOR framework, the Hungarian combinatorial optimisation algorithm improves the match between datasets, while the Jaccard similarity coefficient is effective for measuring the correspondence between the matched data populations. The ARBOR framework was applied to GR and remotely-sensed tree data from a woodland study site to demonstrate how ARBOR can identify the optimum ITC delineation technique, out of four different methods tested, based on two measures of statistical accuracy. Using ARBOR will limit further reliance on arbitrary thresholds as it provides an objective approach for quantifying accuracy in the development and application of ITC delineation algorithms.

10 To assess the accuracy of individual tree crown (ITC) delineation techniques the same tree 11 needs to be identified in two different datasets, for example, ground reference (GR) data and 12 crowns delineated from LiDAR. Many studies use arbitrary metrics or simple linear-distance 13 thresholds to match trees in different datasets without quantifying the level of agreement. For 14 example, successful match-pairing is often claimed where two data points, representing the 15 same tree in different datasets, are located within 5m of one another. Such simple measures 16 are inadequate for representing the multi-variate nature of ITC delineations and generate 17 misleading measures of delineation accuracy. In this study, we develop a new framework for 18 objectively quantifying the agreement between GR and remotely-sensed tree datasets: the 19 Accuracy of Remotely-sensed Biophysical Observation and Retrieval (ARBOR) framework. 20 Using common biophysical properties of ITC delineated trees (location, height and crown 21 area), trees represented in different data sets were modelled as overlapping Gaussian curves 22 to facilitate a more comprehensive assessment of the level of agreement. Extensive testing 23 quantified the limitations of some frequently used match-pairing methods, in particular, the 24 Hausdorff distance algorithm. We demonstrate that within the ARBOR framework, the 25 Hungarian combinatorial optimisation algorithm improves the match between datasets, while 26 the Jaccard similarity coefficient is effective for measuring the correspondence between the 27 matched data populations. The ARBOR framework was applied to GR and remotely-sensed 28 tree data from a woodland study site to demonstrate how ARBOR can identify the optimum 29 ITC delineation technique, out of four different methods tested, based on two measures of 30 statistical accuracy. Using ARBOR will limit further reliance on arbitrary thresholds as it 31 provides an objective approach for quantifying accuracy in the development and application 32 of ITC delineation algorithms. 33

HTTP adaptive video streaming matches video quality to the capacity of a changing context. A variety of schemes that rely on buffer state dynamics for video rate selection have been proposed. However, these schemes are predominantly based on heuristics, and appropriate models describing the relationship between video rate and buffer levels have not received sufficient attention. In this paper, we present a QoE-aware video rate evolution model based on buffer state changes. The scheme is evaluated within a real-world Internet environment. The results of an extensive evaluation show an improvement in the stability, average video rate and system utilisation, while at the same time a reduction in the start-up delay and convergence time is achieved by the modified players.

Observations of tree canopy structure are routinely used as an indicator of tree condition for the purposes of monitoring tree health, assessing habitat characteristics or evaluating the potential risk of tree failure. Trees are assigned to broad categories of structural condition using largely subjective methods based upon ground-based, visual observations by a surveyor. Such approaches can suffer from a lack of consistency between surveyors; are qualitative in nature and have low precision. In this study, a technique is developed for acquiring, processing and analysing hemispherical images of sessile oak (Quercus petraea (Matt.) Liebl.) tree crowns. We demonstrate that by calculating the fractal dimensions of tree crown images it is possible to define a continuous measurement scale of structural condition and to be able to quantify intra-category variance of tree crown structure. This approach corresponds with traditional categorical methods; however, we recognize that further work is required to precisely define interspecies thresholds. Our study demonstrates that this approach has the potential to form the basis of a new, transferable and objective methodology that can support a wide range of uses in arboriculture, ecology and forest science.

For many different investigative purposes, trees and forests are aerially scanned using light detection and ranging (LiDAR). Often, this also requires the manual measurement of ground reference (GR) plots within the LiDAR scan. Upon analysis, there is regularly a mismatch between the alignment of GR and LiDAR tree locations, crown areas and tree heights. This anomaly is frequently overlooked and under-reported in the current literature. This study investigates the suitability of match pairing algorithms for the quantification of misalignment errors between two datasets representing GR and LiDAR data, and recommends an algorithm for accurately quantifying match-pairing differences.

The increased use of mobile devices has prompted the need for efficient mobility management protocols to ensure continuity of communication sessions as users switch connection between available wireless access networks. Locator Identifier Separation Protocol Mobile Node (LISP-MN) was designed to enable such efficient mobility of nodes on the Internet. The protocol enables mobility by ensuring that the IP address used for creating data session is maintained throughout the lifetime of the communication session and the location of the mobile node (MN) is updated as the device moves. While session continuity is achieved during handover, we observed that LISP-MN records loss of packets in transit, long service disruption time, throughput degradation and increased rate of TCP retransmission as an MN conducts a handover from one access link to another. To mitigate the poor handover performance, we introduced a novel network node into the LISP-MN architecture, a loc-server that buffers the packets sent to an MN during handover and forwards to the device upon completion of the movement process. We analysed both qualitative features and quantitative measurements of vanilla LISP-MN against LISP-MN with loc-server support. Results show that the improved architecture significantly improved the performance of LISP-MN in all the investigated parameters.

Host mobility protocols such as Locator-Identifier Separation Protocol Mobile Node (LISP-MN) are known to experience packet loss at the point of handover. For the duration of the handover, packets sent to the MN via the old access link are dropped by the router since it has no way of knowing where the device has moved to. This affects the performance of transport layer protocols of the TCP/IP stack, which results in degradation of network performance. Buffering these packets close to the MN's new location and forwarding them to the MN on handover completion is one way of improving the overall performance of the mobility protocol. Hence, we introduce a novel network node, loc-server, to buffer these packets in order to mitigate the packet loss and reduce the service disruption time (SDT) experienced by MNs during handovers. Using a laboratory testbed implementation, LISP-MN with loc-server support shows significant reduction in packet loss and reduced SDT in comparison to vanilla LISP-MN. Similarly, performance analysis of DASH video player also shows the new architecture helps in improving the average video quality downloaded by the MN and reduces the player's instability.

Video content is increasingly being consumed on the move using mobile devices such as smartphones and tablets. In order to deal with the challenges of heterogeneity of network access technologies and fluctuating resources, which are inherent features of mobile communication, HTTP adaptive streaming (HAS) is becoming the default technology for online video streaming. However, little research has been carried out to better understand the impact of handover schemes of the various mobility management protocols on the video quality of HAS. In this study, the authors present a comprehensive experimental measurement of the impact of handover on three representative HAS players. First, they implement three existing mobility management protocols, MIPv6, LISP-MN and PMIPv6, on a network testbed. Using the fluid flow mobility model, the impact of frequent handover on the average video quality, the bandwidth utilisation and stability of the players was investigated. Their results show a degradation of all the observed parameters in all the reviewed players.

HTTP adaptive streaming (HAS) is the most recent attempt regarding video quality adaptation. It enables cheap and easy to implement streaming technology without the need for a dedicated infrastructure. By using a combination of TCP and HTTP it has the advantage of reusing all the existing technologies designed for ordinary web. Equally important is that HAS traffic passes through firewalls and works well when NAT is deployed. The rate adaptation controller of HAS, commonly called adaptive bitrate selection (ABR), is currently receiving a lot of attention from both industry and academia. However, most of the research efforts concentrate on a specific aspect or a particular methodology without considering the overall context. This paper presents a comprehensive survey of the most significant research activities in the area of client-side HTTP-based adaptive video streaming. It starts by decomposing the ABR module into three subcomponents, namely: resource estimation function, chunk request scheduling, and adaptation module. Each subcomponent encapsulates a particular function that is vital to the operation of an ABR scheme. A review of each of the subcomponents and how they interact with each other is presented. Furthermore, those external factors that are known to have a direct impact on the performance of an ABR module, such as content nature, CDN, and context, are discussed. In conclusion, this paper provides an extensive reference for further research in the field.

The performance of wireless mesh networks (WMNs) deployed for Internet access in rural settings is affected by several factors. Typically, deployments in African domains use cheap and computationally constrained devices with challenges such as power fluctuations, gateway congestion, VSAT communications asymmetry and low bandwidth, which affects throughput under dynamic scenarios. Caching methods can offer improvement for content availability to ensure a reliable quality of experience (QoE) for rural dwellers. Primarily, we integrate a modified multicast technique and overhearing for object caching and cache dissemination. We proposed a Distributed Overheard-object Caching Approach (DOCA) and evaluated the performance employing simulations. The outcome shows significant improvements over the random-path-cache-request (RPCR) strategy with increased data availability and reduced communication cost regarding response time for the outlined rural scenarios. Moreover, the optimization of gateway load helps to conserve network resources such as bandwidth and nodal energy considerably.

Some traffic characteristics like real-time, location-based, and community-inspired, as well as the exponential increase on the data traffic in mobile networks, are challenging the academia and standardization communities to manage these networks in completely novel and intelligent ways, otherwise, current network infrastructures can not offer a connection service with an acceptable quality for both emergent traffic demand and application requisites. In this way, a very relevant research problem that needs to be addressed is how a heterogeneous wireless access infrastructure should be controlled to offer a network access with a proper level of quality for diverse flows ending at multi-mode devices in mobile scenarios. The current chapter reviews recent research and standardization work developed under the most used wireless access technologies and mobile access proposals. It comprehensively outlines the impact on the deployment of those technologies in future networking environments, not only on the network performance but also in how the most important requirements of several relevant players, such as, content providers, network operators, and users/terminals can be addressed. Finally, the chapter concludes referring the most notable aspects in how the environment of future networks are expected to evolve like technology convergence, service convergence, terminal convergence, market convergence, environmental awareness, energy-efficiency, self-organized and intelligent infrastructure, as well as the most important functional requisites to be addressed through that infrastructure such as flow mobility, data offloading, load balancing and vertical multihoming.

The Internet is often thought to be a model of resilience, due to a decentralised, organically-grown architecture. This paper puts this perception into perspective through the results of a security analysis of the Border Gateway Protocol (BGP) routing infrastructure. BGP is a fundamental Internet protocol and its intrinsic fragilities have been highlighted extensively in the literature. A seldom studied aspect is how robust the BGP infrastructure actually is as a result of nearly three decades of perpetual growth. Although global black-outs seem unlikely, local security events raise growing concerns on the robustness of the backbone. In order to better protect this critical infrastructure, it is crucial to understand its topology in the context of the weaknesses of BGP and to identify possible security scenarios. Firstly, we establish a comprehensive threat model that classifies main attack vectors, including but non limited to BGP vulnerabilities. We then construct maps of the European BGP backbone based on publicly available routing data. We analyse the topology of the backbone and establish several disruption scenarios that highlight the possible consequences of different types of attacks, for different attack capabilities. We also discuss existing mitigation and recovery strategies, and we propose improvements to enhance the robustness and resilience of the backbone. To our knowledge, this study is the first to combine a comprehensive threat analysis of BGP infrastructures withadvanced network topology considerations. We find that the BGP infrastructure is at higher risk than already understood, due to topologies that remain vulnerable to certain targeted attacks as a result of organic deployment over the years. Significant parts of the system are still uncharted territory, which warrants further investigation in this direction.

Future wireless networks need to offer orders of magnitude more capacity to address the predicted growth in mobile traffic demand. Operators to enhance the capacity of cellular networks are increasingly using WiFi to offload traffic from their core networks. This paper deals with the efficient and flexible management of a heterogeneous networking environment offering wireless access to multimode terminals. This wireless access is evaluated under disruptive usage scenarios, such as flash crowds, which can mean unwanted severe congestion on a specific operator network whilst the remaining available capacity from other access technologies is not being used. To address these issues, we propose a scalable network assisted distributed solution that is administered by centralized policies, and an embedded reputation system, by which initially selfish operators are encouraged to cooperate under the threat of churn. Our solution after detecting a congested technology, including within its wired backhaul, automatically offloads and balances the flows amongst the access resources from all the existing technologies, following some quality metrics. Our results show that the smart integration of access networks can yield an additional wireless quality for mobile flows up to thirty eight percent beyond that feasible from the best effort standalone operation of each wireless access technology. It is also evidenced that backhaul constraints are conveniently reflected on the way the flow access to wireless media is granted. Finally, we have analyzed the sensitivity of the handover decision algorithm running in each terminal agent to consecutive flash crowds, as well as its centralized feature that controls the connection quality offered by a heterogeneous access infrastructure owned by distinct operators.

In order to streamline video content distribution on a myriad of platforms over heterogeneous networks, HTTP Adaptive Streaming (HAS) is being increasingly adopted. In this paper we pilot a bio-inspired HAS optimisation design with the aim of maximising the overall user experience of a video playback session. Evaluations conducted within a real-world Internet environment, using quality indicators such as convergence time, start-up delay, average video rate, stability, and fairness, demonstrate the benefits of our design.

This article investigates the usage of digital channels by UK small-and medium-sized enterprises (SMEs) and assesses the impact caused on their strategic marketing position. The research is based on statistical analysis of 66 surveyed SMEs in the context of the digital era. Despite indications from the relevant literature about the reluctance of SMEs to adopt advances in technological communication, the research reported indicates a high level of usage of digital channels, especially social media (SM). The web 2.0 technologies that facilitate the new digital channels are standardised, interactive, ubiquitous and cheap. These features change the way how companies communicate and shift fundamental marketing and business concepts. Due to this shift, the SMEs' barriers for technology adoption, including lack of financial resources, knowledge and skills, are diminishing. The latter, supported also by the research findings, increases the impact of SMEs bringing them closer to the large corporations in the global marketplace. The study is significant because it extends previous knowledge on technology adoption, with findings about the adoption of digital channels by SMEs, but more importantly, it opens up a novel insight into strategic literature for SMEs.